[FEATURE] support plan mode

## Feature Description

When in plan mode, claude asks to review the plan in Nvim like following.
```
ctrl-g to edit in Nvim · ~/.claude/plans/optimized-marinating-scott.md
```
I'd like this to open up in my connected nvim session.
Currently ctrl-g just fires up a new nvim session inside cc terminal.

## Use Case

ability to edit plan in connected nvim session

## Proposed Solution

If you have ideas about how to implement the feature, share them here.

## Alternatives Considered

Have you considered any alternative solutions or workarounds?

## Additional Context

Add any other context, screenshots, or examples about the feature request here.